Low density high-strength boron on beryllium reinforcement filaments

ABSTRACT

A HIGH-STRENGTH LOW-DENSITY CONTINUOUS FILAMENT HAVING A DENSITY OF ABOUT 2G./CC. A TENSILE STRENGTH OF MORE THAN 100,000 P.S.I. AND A MODULUS OF ELASTICITY OF MORE THAN 20X106 P.S.I. IS FORMED FROM A BERYLLIUM WIRE SUBSTRATE OF ABOUT FIVE MILS DIAMETER WITH A BORON COATING OF ABOUT TWO MILS THICKNESS, THE FILAMENT IS PREPARED BY VAPOUR PHASE DEPOSITION FROM DIBORANE IN AN INERT GAS AFTER THE BERYLIUM IS ETCHED AND ELECTRICALLY HEATED TO ABOUT 400* C. THE COATED FILAMENT IS SLOWLY HEATED AND COOLED.

United States Patent 3,741,797 LOW DENSITY, HIGH-STRENGTH BORON ON BERYLLIUM REINFORCEMENT FILAMENTS Nicholas H. Chavasse, Jr., Forestville, and James C.

Withers, Accokeek, Md., assignors to General Technology Corporation, Alexandria, Va.

No Drawing. Continuation of abandoned application Ser. No. 621,767, Mar. 9, 1967. This application Apr. 30, 1970, Ser. No. 31,839

Int. Cl. C23c 11/00 US. Cl. 117-106 R 4 Claims ABSTRACT OF THE DISCLOSURE A high-strength low-density continuous filament having a density of about 2 g./ cc. a tensile strength of more than 100,000 p.s.i. and a modulus of elasticity of more than 20 10 p.s.i. is formed from a beryllium wire substrate of about five mils diameter with a boron coating of about two mils thickness. The filament is prepared by vapor phase deposition from diborane in an inert gas after the beryllium is etched and electrically heated to about 400 C. The coated filament is slowly heated and cooled.

This application is a continuation of application Ser. No. 621,767, filed Mar. 9, 1967, now abandoned.

This invention relates to low density, high-strength boron on beryllium reinforcement filaments and to a method of making the same. The method comprises contacting a beryllium wire substrate with a mixture of diborane in an inert gas at a temperature of about 350-550 C.

Numerous reinforcement filaments of high-strength have have been made in the past. Such filaments comprise a fine substrate wire on which is deposited a thick coating of the high-strength material. Typical substrate material are high-temperature resistant metals, such as tungsten or molybdenum. The coating materials have been chosen from among metallic and non-metallic elements, oxides, carbides, borides, silicides and nitrides. Typical coating materials are boron, silicon carbide, boron carbide, boron silicide, aluminum nitride and the like.

Such high-strength reinforcement filaments are prepared generally by heating the substrate wire to an elevated temperature suitable for deposition of the coating material thereon from a gaseous source of the coating material. The substrate is usually heated to the desired deposition temperature by passing electric current therethrough. Then the heated substrate is contacted with the gaseous source of the coating material whereupon the coating material is deposited upon the substrate.

For use in many structural bodies, e.g. aircraft, it is desirable that the reinforcement filament exhibit a low density as high-strength properties. However the substrate wire of the prior art reinforcement filaments possesses a very much higher density that the coating material itself. Therefore, to minimize the overall density of the filament, the diameter of the substrate must be made small composed to the diameter of the coating thereon. Specifically, the substrate usually comprises only a few percent of the cross-sectional area of the filament. Thus the density of the filament approaches, but does not reach, the density of the coating material itself.

Accordingly, it would be particularly desirable to provide high-strength, reinforcement filaments which utilize a substrate which has an extremely low density, in fact, which is lower than any substrate material presently used in similar filaments.

It is an object of the present invention, therefore, to provide a high-strength, reinforcement filament having a very low density, and, preferably, in which the density of the substrate is lower than that of the coating material.

3,741,797 Patented June 26, 1973 In order to be a practical reinforcement filament it is also necessary that the coating material be compact, uniform, and firmly adherent to the substrate, and stable both physically and chemically towards deterioration in air and at elevated temperatures.

Another object of the invention, therefore, is to provide a low density, high-strength, reinforcement filament in which the coating material is strongly adherent to a low denstiy substrate material, and compact, uniform and stable.

A specific object of the invention is to provide a low density, high-strength, reinforcement filament comprising a compact, adherent, uniform coating of a high-strength material, for example, boron, on a beryllium substrate.

Yet another object of the invention is to provide a method of making a boron on beryllium filament having the aforementioned advantageous properties and physical characteristics.

These and other objects of the invention will be made apparent from the following more particular description of the invention in which reference will be made to certain specific embodiments thereof.

In accordance with the present invention, there is provided herein a low density, high-strength reinforcement filament comprising a compact, adherent, uniform coating of boron on a beryllium substrate. The boron-beryllium filaments produced herein are extremely light in weight, but are able to withstand corrosion, high temperatures, and great stresses. The filaments usually are made continuous in length, and then are cut to any desired given length for use in a given reinforcement application. For this purpose a plurality of the filaments may be embedded in a matrix material to form a composite article of manufacture. One particularly useful application for the filaments of this invention is in the manufacture of components where weight is a critical part of the design and construction.

In general, the boron-beryllium filaments of the present invention are made by depositing a boron coating onto a beryllium wire substrate by chemical deposition from the vapor phase. In order to produce adherent, uniform coatings of boron on the beryllium substrate, it is preferable to carry out the process in a certain manner, including a number of process steps, particularly with re spect to the conditions of deposition.

First a beryllium wire substrate is provided in the form of a fine Wire of constant diameter. A typical beryllium wire substrate has a diameter of about 5 mils. The beryllium wire usually is pretreated by etching in an acid bath prior to insertion in the deposition chamber. A typical etching solution comprises a mixture of 450 ml. of conc. phosphoric acid, 25 ml. conc. sulfuric acid and 52 grams of chromic oxide. Other etchants which remove surface oxides and contaminants from the beryllium substrate may be used as well, as for example, 25% HF. The etching is carried out at a temperature of 25 to 200 C. for l-10 minutes. The rate of etching is about 0.1 to 0.5 mil per minute at a temperature of 25 C. At the end of the etching period the beryllium wire is thoroughly rinsed in water and placed in the deposition chamber.

The next step in the process is to deposit the boron coating on the etched beryllium wire substrate. The beryllium filament is supported in the deposition chamber between two electrodes, and slowly heated to the deposition temperature by electric heating means. The deposition temperature is about 350-550 C., and preferably 385 425 C., with the more nearly optimum temperature being closer to the lower end of the preferred range.

The boron deposition preferably is carried out from a mixture of diborane in an inert gas, for example, argon. Any suitable concentration of diborane may be used. Preferably a concentration of about 1-5 percent diborane is used for this purpose. The flow rate is about 1 to 1.2 s.c.f.h. A deposition period of about two minutes produces a boron coating of about 0.5 to 1 mil on the beryllium substrate. Thicker coatings are obtained after longer deposition periods.

The resulting boron on beryllium filament then is slow ly cooled to room temperature. Preferably the filament is cooled to room temperature over a period of at least a minute. Finally the filament is removed from the deposition chamber.

The boron-beryllium filament thus produced is characterized by comprising a compact, firmly adherent, uniform coating of boron on a beryllium wire substrate. Such a filament has the following physical properties:

Diameter of beryllium substrate: 5 mils Thickness of boron coating: 2 mils Diameter of resultant filament: 7 mils Ratio of diameter of resultant filament to diameter of beryllium substrate: 1.4

Ration of volume of boron to volume of resultant filament: .49

Density of beryllium substrate: 1.8 g./cc.

Density of boron coating: 2.0-2.3 g./cc.

Density of resultant filament: 2.0 g./cc.

Tensile strength of resultant filament: 100,000-400,000

Modulus of elasticity of resultant filament: 30 to 50x10 The boron or beryllium filament of the present invention finds wide application in composite manufacture as a low density, high-strength, reinforcement material.

What is claimed is:

1. A low density, high tensile strength reinforcement filament comprising a beryllium wire substrate having an etched surface on which a compact, uniform coating of boron is firmly adherent, said filament having a tensile strength of at least about 100,000 p.s.i.

2. A filament of claim 1 wherein said boron coating is at least about 0.5 mil thick.

3. A filament of claim 1 wherein said boron coating has a density of from about 2.0 to about 2.3 g./cc.

4. A filament of claim 1 wherein said filament has a density of about 2 g./cc.

References Cited UNITED STATES PATENTS 2,528,454 10/1950 Schlesinger et a].

3,123,493 3/ 1964 Brick.

3,365,330 1/ 1968 Hough.

3,409,469 11/1968 Kuntz.

3,451,840 6/1969 Hough 107106 X OTHER REFERENCES Powell et al., Vapor Plating, 1955. Powell et al., Vapor Deposition, 1966.

ALFRED L. LEAVITT, Primary Examiner U.S. Cl. X.R. 117-128, Dig. 10 

